Agitator



Oct. 8, 1968 R. K. MULTER 3,404,870

AGITATOR Filed Sept. 23, 1965 5 sheets-sheet 1 INVENTOR QM 4 Mae;

Oct. 8, 1968 R. K. MULTER 3,404,870

AGITATOR Filed Sept. 23, 1965 5 Sheets-Sheet 2 FIG. 2

Oct. 8, 1968 R. K. MULTER 3,404,870

AGITATOR Filed Sept. 23, 1965 5 Sheets-Sheet 5 /NVNTOR 434 k, mwu;

Oct. 8, 1968 v R. K. MULTER 3,404,870

AGITATOR Filed Sept. 23, 1965 5 Sheets-Sheet 4 WW. W

INVENTOR.

ROBERT K. MU LTER Oct. 8, 1968 R. K. MULTER 3,404,870

, AGITATOR Filed Sept. 235, 1965 5 $heetsSheet 5 INVENTOR.

ROBERT K. MULTER i I Robert K. Multer,

States I Pa entbific 7 3,404,810 AGITATOR RED 1, Colts'Neck, NJ. 07722Filed Sept. 23, 1965, Ser. No. 489,632

' 8 Claims. (Cl. 25943)' This invention relates to apparatus foragitating a liquid mixture, and more particularly to an impeller forsuch apparatus, especially suited for blending liquids, and forv mixingandsuspending particles and fluids in aliquid material, and formaintaining such mixtures in a state of uniform dispersion.

=-A great variety of apparatus for the agitation of liquids has beendeveloped over the years, because. this opera- .tion has been requiredinalmost every industry. Many kinds continue in use today, ,butmost havecertain features in common.

Theliquids under agitation are usually driven by one or morepowered,.rotating impellers, and the operation is usually carried out ina vessel with a circular cross-seclion and a vertical axis. Extensiveengineering literature on the subject classifies the liquid agitatingsystems according to the typefof flo'w developed by the impeller:rotational, axial, or radiaL,

Amongthe oldest agitators are many rotational impeller systems. Theimpeller generally comprises onepr more flat, vertically-surfacedpaddles, radiating from 'a central driving shaft, which drives theliquid around horizontally. Vertical and radial flow, and liquid shear,are minimal unless the basic design is modified with stationary orcontra-rotating surfaces inserted in the liquid flow path.

Probably todays most common agitator for smaller vessels is thevertical-shaft screw propeller system, "in which the liquid is drivendownward in a narrow, cylindrical path near the central axis of thevessel. Thepflow is diverted radiallyby the bottom of the vessel, andthen upward by the wall, of the vessel, eventually to return radiallyinward at the upper surface of the agitated liquid. This vertical andradial motion is generated only when rotation of the liquid is inhibited'by stationary bafl1es,'or

v Like conventional agitators, .mine'.. o ften.-.requires t ,sta-

counteracted by tilting of the impeller shaft sothat the axial flow fromthe propeller opposes the rotational flow.

In larger vessels, liquids are often agitated with horizontal-shaftscrew'propellers, which drive the liquid along straight, approximatelyradial paths. Usually aft'erbei'ng driven across the bottom of thevessel the liquid is di-' verted upward and tangentially by the wall ofthe vessel,

to return across the 'surfac"e'of the liquid and downward to thepropeller.

The most common agitators for generating radial flow are the centrifugaltype, including blade turbines, discs,

cones, cylinders, etcl, which drive the liquidoutwardby friction andcentrifugal force, near the bottomof the vessel, when rotated rapidly ona vertical shafL'The liquid is diverted upward'by the wall, eventuallyto return 'instrongly unless' rotation of the liquid is inhibitedby-stationary bafiles. a Another well-known agitator for generatingradial "flow 'ward and downward to the impeller. As with theverticalshaft propellers, vertical and radial flow does not persist isthe radial propeller, in which a vertical shaft has hori--.

zontal arms at the ends of which are flat, vertical pumpingblades whichare pitched so as to drive the liquid'outward. The flow path is likethatfor the centrifugal impelle'rs.

A good apparatus for'agitating aliquid mixture will set the entire massof liquid incontinuousmotiongwith a uniform distribution of velocitythroughout. The im- "peller must be designed'to generate therequired-mixing,

dispersing, and suspending action with minimum power consumption.For'uniformity in the product and-for high -wasting agitation anywhere.

Patentedv Oct. 8, 1968 "Advantages-soughtin-an agitatordesign includeability to produce the desired'mixture quickly and -to maintain'it"perpetually, low power consumption, durability, ease of *cleaning andmachine maintenance, feasibility of'constructionfrom a wide variety ofmaterials, low cost of construction, andfiexibility in major operatingvariables such as type of liquid and height of liquid in the vessel. Myinvention provides an improved balance :ofthese advantages by-impellingthe liquid in'a different-"manner. My impeller drives the liquidupward,adjacent to and 'parallel to the wall of the vessel, from all points inanarea around the circumference. of the bottom of the .vessel, whilesweeping closely over the remaining'area of; the bottom. The impeller isslow-turning, dynamically-stable, light in weight; easilyconstructed,.efiicientinuse of power, and versatile; .s .r Th-isimpeller comprises any-number-of flat, horizontal arms that rotate .ina. single horizontal plane, eachiarm bearing'dat its-outer endan.--upward-pitched blade,, ;the whole beingsupported and rotatedbyasingle-, -vertical shaft'at the axis of. a cylindrical-vessel."

-Two.blades, on'the ends of.a pairof. in-line arms, .are often adequate.These would be installed as closefas possible to the bottom-of the.-vessel,:lwith theblade'tips as *closeas possible to the wall. vAdditionalsarms and blades'maybe, placed in this'same plane. Additionalimpeller-sets may b.eattached to vthe shaft-at highertlocationsw 1tionary baffles that inhibit rotation. of thezliquid';

"'The large diameteryof the impeller resultsgin high tip speeds at lowrates of rotation. .Thecombination, of large diameter withlow rates ofrotation produces great-dynamic stability; The high tip speedsmake-possible transfenof large-amounts of energy-to the liquid,withnonly a slight "pitch to'the' blades; This low pitch angle=yieldshigh power efficiency and reduces-shock loads and damage; to fragile'-S.olid"particles. l a

Outboard-bearings, submerged thev liquid, are usually not needed, evenin very large systems. -,,,In.the -drawings fIG. -1;is,aside,.e1evational view, in

.section, showinga ,typical agitating system. incorp0rat in g myimpeller. ,FI G 2 is a planview.-of,a..double b1ade impellennwith a pairofin-line. arms, in,a -typic al impellerc el configura o i vqp io bafi eand bra i ;FIG. .3 is;a fragmentaryside, elevatio nal View. of: theimpeller of-. FI G.,-2 including an optional, brace.

4 isan end-yiew Of atypical impeller bladeand :.a rm ;0na shaft; I

5 isra fragmentary-side elevational-iview, .in section, 1 showing; atypical side-outlet. drain mounted; inthe -.wall, ofa cylindricalvesself u .1 I F166 is a side elevational view, in seetion showsingexample; :of ;an agitating, .-system incorporating numerous ,sets, ofbladeebearing-armstatvarious elevations alongathe the shaft 2, with theminimum feasible clearance above the H bottom of the vessel 1. a

The pitched tips or blades at the ends of these arms are brought asclose as feasible to the wall of the vessel. Dimensions of one or twoinches for bottom and end clearance are typical, but these may bevaried.

One or more baffles 7 may be mounted rigidly inside the vessel, withthree or four being typical. These baffles ordinarily should be set asclose as possible to the bottom of the vessel, and should usually extendupward to a height close to the liquid surface, but not so high as tocause the liquid to splash over the vessel wall. An opening 8 in thebaflle is generally desirable to eliminate stagnant pockets and toprevent solid material from adhering to the wall and battle. A goodwidth for the baflle in the radial direction is about one-third of thevessel radius, but this, and all other baflle dimensions, and the numberand shape of bafiles, may be varied without changing the kind ofagitation generated by my impeller.

The vessel 1 shown in FIG. 1 is a conventional, vertical, cylindricaltank, with diameter about equal to the height. The dimensions of thisvessel may be varied according to ordinary engineering practice, whichgenerally prescribes a diameter equal to between one-third and threetimes the height. The advantages that derive from the use of my impellerand the agitating systems which utilize my impeller are generallymaintained regardless of variations in size and shape of the vessel.

When the impeller is rotated, the liquid follows a path 9 like thatshown in FIG. 1: rising near the wall, radially inward at the surface,sinking near the shaft, and radially outward along the bottom. There mayalso be some rotation of the liquid, depending on the type of fluid, thenature of the baffling, the impeller speed, the depth of liquid, andother factors.

This pattern of liquid motion will not ordinarily change much, in awell-proportioned system, as the depth of liquid changes. However invery flat, shallow vessels, or when the liquid level is extremely low inany vessel, the flow will not strictly follow the pattern shown; inthese cases there will be an exceptional amount of turbulence,

rotation, and centrifugal action because of the close proximity of theimpeller arms to the liquid surface.

In very tall, narrow vessels it may be desirable to place additionalimpeller arms with blades at various heights along the shaft. For mostapplications, only one, doublebladed pair of arms is required at anylevel.

In FIG. 6, three sets of blade-bearing arms 12 are shown at variouselevations along the shaft 2.

For some applications, as in vessels with very large diameters,additional bladed arms in the same horizontal plane may be desirable.

In FIG. 7, a three-blade impeller set 13 is shown. In FIGS. 8 and 9 areshown a four-blade impeller set 14, and a six-blade impeller set 15,respectively. In each of these three examples, all of the blades andarms in a set are in a single plane.

It should be emphasized that many of the benefits of my impeller andagitating system derive from the fact that in most vessels, with mostfluids, and regardless of variations in operating depth, only two bladeson a pair of in-line arms are needed.

FIG. 2 shows how arm 6, shaft 2, and blades appear when typicallyinstalled in a vessel 1 which includes one optional baffle 7 with awall-side opening 8. Optional brace 11 is desirable for stiffening armsmade of thin material. Two arms can be formed from a single, fiat strip,with its narrow edge facing in the direction of motion; the blades 10can then be formed by twisting orv bending the outer extremities of thearms as shown in the drawings, or separate blades can be attached.

Bracing of the arms is desirable, because this permits the use ofthinner material, not only reducing weight, but also reducing rotationof the liquid and improving the effectiveness of the arms in cuttingthrough solids or viscous fluids at the bottom of the vessel.

The particular brace 11 shown also improves the agitation. This brace ismade from a flat strip, approximately the same in cross-section as thearm 6. The brace is twisted through so that its inner end may befastened to the shaft in a vertical plane, while its outer end may befastened in a horizontal plane to the arm 6 next to the blade 10. Iftwisted in the correct direction, the brace will impel liquid downwardnear the shaft during normal rotation, and will also generate someradial flow by centrifugal action near the shaft.

FIG. 3 shows in detail a typical assembly of shaft 2, arm 6, blade 10,and twisted brace 11. The normal direction of rotation would be towardthe viewer.

FIG. 4 shows an end view of an impeller blade 10 formed by twisting anarm made of a flat strip. The blade is bent upward, so that the entirelength of the arm and blade may closely follow the flat bottom of atank, The pitch should normally be about 10 to 15 from the horizontal,but this can be varied.

In general, the pitched blade of the impeller should extend over aboutthe outer one-third of the radius of the vessel. The width of the flatside of the arm and blade can be about one-thirtieth of the vesseldiameter.

Rotational speed depends on the kind of agitation desired, the kind offluid, the size of the vessel, and the exact impeller configuration,among other variables. I have found that a speed of about 40 to 50revolutions per minute gives good agitation of the aqueous dispersionsin tanks whose diameters are 5 to 7 feet, when all other proportions areabout as described in the foregoing.

All of the dimensions, proportions and speeds described herein may bealtered considerably, without departing from the essential concept ofthis invention, which is to use a simply-formed, large-diameter,rotating blade impeller, pitched upward at its outer extremities, so asto impart upward motion to a liquid from points near the bottom of thewall of a vertical, cylindrical vessel, for the chief purpose of mixing,dispersing, suspending, and otherwise agitating fluids and fluidmixtures in vessels of all sizes.

My impeller and agitating system have numerous advantages over previousdesigns, which will affect the way my invention will be used, and willgovern the specific details of its construction in actual applications.

The impeller performs well in simply-built, flat-bottomed tanks, withstraight, vertical sides, and plain, sharp corners at the junction ofwall with bottom. These tanks are usually the easiest and cheapest tobuild, but conventional agitators do not perform well in them. Not onlydoes my impeller agitate all parts of such vessels, but it also promotesenhanced drainage despite the lack of slope. Furthermore, well-mounted,side-outlet drains may be used with my agitation system, eliminating theneed for supports which raise the tank above the floor to provide forthe usual, center-mounted drains.

FIG. 5 shows the tip of the impeller blade heretofore described sweepingclosely past the mouth of a typical side-outlet drain 16, so that thedrainage from a flatbottomed vessel through such a drain is facilitatedand made more complete than with other impeller designs.

Despite its suitability for flat-bottomed vessels, the impellerdescribed here is easily modified to fit closely to a bottom of almostany shape.

The simple shape of this impeller, the lack of precision needed in itsfabrication, and its dynamically stable shape, make possible theconstruction of units of any size, without complex tools or highlyskilled labor, using standard shapes of almost any constructionmaterial, and applying protective coatings when required.

The T shape can be inserted through small openings in avessel, or thearms can be attached to the shaft after both have been insertedseparately into the vessel.

Bearing and support requirements are not severe, even when shafts arelong, diameters large, and power high.

Outboard bearings submerged in the liquid are not needed.

Power consumption is low.

The impeller generates such uniform motion throughout the entire vessel,even while the speed is varied through a wide range, that the degree ofagitation is easily adjusted without sacrifice in completeness ofagitation throughout the vessel.

Because the impeller sweeps the entire bottom of the vessel, heavymaterials cannot remain there undisturbed. Materials that settle arecontinually lifted, fluidized, and carried radially to the blades forelevation.

Since the liquid is initially placed in motion by being driven directlyupward, adjacent to the smooth side wall of the vessel, it easilycontinues in motion all the way to the upper surface, even in tallvessels. The fluid is not forced through right-angle turns before beinglifted, as it is with other agitators.

Heavy materials which fall prematurely out of the rising stream arequickly relifted, while well-suspended materials follow the longestpossible path.

Adhesion of suspended materials to the vessel is mini mized, becauseflow is largely directed parallel to vessel surfaces, rather thanperpendicular as with conventional agitators.

The impeller is uniquely effective when the depth of liquid is very low,because centrifugal action drives most of the liquid to the outer rim,where the blades and baflies can function. Splashing and foaming areminimized under such conditions because the arms are so close to thebottom. Conventional agitators cease to function, and may causeexcessive splashing and foaming at very low levels, because they operatenear the center of the vessel, and usually not as close to the bottom asmine.

The small cross-section of my impeller in the direction of motion helpsreduce the size of large particles which are to be dispersed, andreduces shock loads on the apparatus.

This small cross-section, and the sweeping action over the entirebottom, make my system effective in resuspending materials which havesettled to the bottom, as for instance during a power failure. If theagitator has suflicient power to cut a path through the settledmaterial, it will eventually redisperse it. On the other hand, if itlacks such power, but has been properly designed to withstand the torqueof its drive and support apparatus, it will not rotate and will not bedamaged. Most conventional designs either will not re-disperse materialsunder such condiitons, or else may be damaged during startup.

The plain shape of the impeller, with its smooth, flat surfaces and alack of undercuts, promotes easy cleaning, and minimizes adhesion ofmaterials during use. Close proximity of the bottom of the vesselminimizes buildup beneath the impeller.

The low velocity of the liquid at the surface, and its predominantlyinward direction, minimizes splashing when the vessel is full. The lackof rotation also minimizes vortex action, which can draw undesired airinto the liquid, but downward flow of liquid at the center is strongdespite the absence of vortex.

The impeller can tolerate much wear and damage without loss ineffectiveness.

Power consumption declines as the liquid depth falls in any vessel, sooperating costs remain in proportion to the productive work performed,and the degree of agitation remains fairly constant.

A single piece of equipment can accommodate a wide variety of fluids andagitation requirements, with no more than a change in speed. Since thedrive and bearing re quirements are so mild, the system can be poweredby V-belt and other simple types of apparatus which permit easy speedchanges.

I claim:

1. An agitator for liquids comprising a vessel and an axial impellersuspended concentrically therein, the impeller comprising a verticalrotatable shaft with two inline opposed arms carried radially by thisshaft and an impeller blade affixed radially and substantiallyhorizontally to the outer end of each of these supporting arms,

(a) the vessel being a right circular cylinder whose axis is verticaland whose bottom is flat and horizontal, and

(b) the length of each arm being about two-thirds of the radius of thevessel, each arm being made of a thin strip of flat material whosegreater width lies in the horizontal plane of rotation and whosethickness in the vertical direction is so small that the hydraulicresistance in the direction of rotation is too slight to generatesubstantial rotary motion of the fluid under treatment, and the plane ofrotation of the arms being adjacent to the bottom of the vessel so thatsediment cannot accumulate to any significant depth beneath the rotatingarms, and

(c) the length of each blade being about one-third of the radius of thevessel so that the outer tips of the blades rotate in close proximity tothe wall of the vessel, the blades being made of flat material similarin shape to that of which the arms are made, with their thin leadingedges rotating in the plane of the arms adjacent to the bottom of thevessel, and with their trailing portions twisted upward behind a linconnecting the leading outer corner of the blade with the trailing innercorner of the blade so .that the rearward surface of the blade comprisesan approximately triangular plane inclined upward at an angle of about10 to 15 from the horizontal plane of rotation of the arms while theforward surface of each blade comprises an approximately triangularplane in the plane of rotation of the arms.

2. The agitator of claim 1 wherein additional identical blades and armsare carried by the shaft in the horizontal plane of rotation adjacent tothe bottom of the vessel.

3. The agitator of claim 1 wherein additional identical sets of bladesand arms are carried by the shaft in horizontal planes of rotation abovethe set of blades and arms described.

4. The agitator of claim 1 wherein no foot bearing is employed tostabilize the lower end of the shaft in relation to the bottom of thevessel.

5. The agitator of claim 1 wherein stationary, vertical bafile surfacesare mounted radially inside the wall of the vessel.

6. The agitator of claim 1, wherein a diagonal brace connects eacharm-blade pair with the shaft, the brace comprising a flat strip whoseends have been twisted perpendicular to each other,with asmoothly-curving surface between the two ends, and so affixed to theimpeller that the widest surface of the brace is vertical at the shaftand horizontal where it joins the arm at the junction of arm and blade,and being twisted in such direction that the brace has itsdownward-driving face in the forward direction during rotation of theimpeller.

7. The agitator of claim 1 wherein the rotational speed is about 40 to50 revolutions per minute in vessels whose diameters are about 5 to 7feet.

8. The agitator of claim 1 wherein a side-outlet drain is mounted in thewall of the vessel.

References Cited UNITED STATES PATENTS 683,474 10/ 1901 MacKinzie 259-44754,931 3/ 1904 Meyrick 259--24 1,803,446 5/1931 Warrick 259-1082,235,604 3/1941 Brumagin 259107 78,398 5/1869 Schuffert et al 259583,572 1/1867 Gordon et al 259108 FOREIGN PATENTS 13,784 1893 GreatBritain. 590,635 4/ 1959 Italy.

WILLIAM I. PRICE, Primary Examiner.

1. AN AGITATOR FOR LIQUIDS COMPRISING A VESSEL AND AN AXIAL IMPELLERSUSPENDED CONCENTRICALLY THEREIN, THE IMPELLER COMPRISING A VERTICALROTATABLE SHAFT WITH TWO INLINE OPPOSED ARMS CARRIED RADIALLY BY THISSHAFT AND AN IMPELLER BLADE AFFIXED RADIALLY AND SUBSTANTIALLYHORIZONTALLY TO THE OUTER END OF EACH OF THESE SUPPORTING ARMS, (A) THEVESSEL BEING A RIGHT CIRCULAR CYLINDER WHOSE AXIS IS VERTICAL AND WHOSEBOTTOM IS THAT AND HORIZONTAL, AND (B) THE LENGTH OF EACH ARM BEINGABOUT TWO-THIRDS OF THE STRIP OF THE VESSEL EACH ARM BEING MADE OF ATHIN STRIP OF FLAT MATERIAL WHOSE GREATER WIDTH LIES IN THE HORIZONTALPLANE ROTATION AND WHOSE THICKNESS IN THE VERTICAL DIRECTION IS SO SMALLTHAT THE HYDRAULIC RESISTANCE IN TH DIRECTION OF ROTATION IS TOO SLIGHTTO GENERATE SUBSTANTIAL ROTARY MOTION OF THE FLUID UNDER TREATMENT, ANDTHE PLANE OF ROTATION OF THE ARMS BEING ADJACENT TO THE BOTTOM OF THEVESSEL SO THAT SEDIMENT CANNOT ACCUMULATE TO ANY SIGNIFICANT DEPTHBENEATHA THE ROTATING ARMS, AND (C) THE LENGHT OF EACH BLADE BEING ABOUTONE-THIRD OF THE RADIUS OF THE VESSEL SO THAT THE OUTER TIPS OF THEBLADES ROTATE IN CLOSE PROXIMITY TO THE WALL OF THE VESSEL, THE BLADESBEING MADE OF THAT MATERIAL SIMILAR IN SHAPE TO THAT OF WHICH THE ARMSARE MADE, WITH THEIR THIN LEADING EDGES ROATATING IN THE PLANE OF THEARMS ADJACENT TO THE BOTTOM OF THE VESSEL, AND WITH THEIR TRAILINGPORTIONS TWISTED UPWARD BEHIND A LINE CONNECTING THE LEADING OUTERCORNER OF THE BLADE WITH THE TRAILING INNER CORNER OF THE BLADE SO THATTHE REARWARD SURFACE OF THE BLADE COMPRISES AN APPROXIMATELY TRIANGULARPLANE INCLINED UPWARD AT AN ANGLE OF ABOUT 10* TO 15* FROM THEHORIZONTAL PLANE OF ROATATION OF THE ARMS WHILE THE FORWARD SURFACE OFEACH BLADE COMPRISES AN APPROXIMATELY TRIANGULAR PLANE IN THE PLANE OFROTATION OF THE ARMS.